Devices have heretofore been provided which are capable of detecting corrosion pits or the like but such devices have generally been insensitive to pits to be detected, especially when the device is located at a substantial spacing distance from a surface in which the pits are to be detected. The prior art devices have also been relatively expensive to construct and they have not been suitable for use in many applications. A particular problem relates to the detection of pits or the like with a moving probe device and especially when there may be a variation in spacing between the probe and the surface in which the pits are to be detected.